That is not how this is supposed to work (you're mixing up make targets with... whatever you're trying to do here), and even if you were doing it the right way, it won't work, unless you're already running a patched kernel, which you're not, since you're currently running a brick ^^.
(Because the factory/recovery updater is handled via the kernel's initrd recovery shell, and that one obviously doesn't recognize our signing key).
As a sidebar, you don't need to build KindleTool, there are binaries available in the
snapshots thread.
As a second sidebar, fastboot images have *nothing* to do with Kindle update packages in the first place. So, that's a big nope on *at least* three fronts.